Doping Copper Atoms into the Nanocluster Kernel: Total Structure Determination of [Cu30Ag61(SAdm)38S3](BPh4)

Chemical Flexibility of Atomically Precise Metal Clusters

Ligand-protected metal clusters possess hybrid properties that seamlessly combine an inorganic core with an organic ligand shell, imparting them exceptional chemical flexibility and unlocking remarkable application potential in diverse fields. Leveraging chemical flexibility to expand the library of available materials and stimulate the development of new functionalities is becoming an increasingly pressing requirement. This Review focuses on the origin of chemical flexibility from the structural analysis, including intra-cluster bonding, inter-cluster interactions, cluster-environments interactions, metal-to-ligand ratios, and thermodynamic effects. In the introduction, we briefly outline the development of metal clusters and explain the differences and commonalities of M(I)/M(I/0) coinage metal clusters. Additionally, we distinguish the bonding characteristics of metal atoms in the inorganic core, which give rise to their distinct chemical flexibility. Section 2 delves into the structural analysis, bonding categories, and thermodynamic theories related to metal clusters. In the following sections 3 to 7, we primarily elucidate the mechanisms that trigger chemical flexibility, the dynamic processes in transformation, the resultant alterations in structure, and the ensuing modifications in physical-chemical properties. Section 8 presents the notable applications that have emerged from utilizing metal clusters and their assemblies. Finally, in section 9, we discuss future challenges and opportunities within this area.

A 66-Nuclear All-Alkynyl Protected Peanut-Shaped Silver(I)/Copper(I) Heterometallic Nanocluster: Intermediate in Copper-Catalyzed Alkyne-Azide Cycloaddition

Ligand-protected heterometallic nanoclusters in contrast to homo-metal counterparts show more broad applications due to the synergistic effect of hetero-metals but their controllable syntheses remain a challenge. Among heterometallic nanoclusters, monovalent Ag-Cu compounds are rarely explored due to much difference of Ag(I) and Cu(I) such as atom radius, coordination habits, and redox potential. Encouraged by copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction, comproportionation reaction of Cu(II)X2 and Cu(0) in the presence of (PhC≡CAg)n complex and molybdate generated a core-shell peanut-shaped 66-nuclear Ag(I)-Cu(I) heterometallic nanocluster, [(Mo4O16)2@Cu12Ag54(PhC≡C)50] (referred to as Ag54Cu12). The structure and composition of Ag-Cu heterometallic nanocluster are fully characterized. X-ray single crystal diffraction reveals that Ag54Cu12 has a peanut-shaped silver(I)/copper(I) heterometallic nanocage protected by fifty phenylacetylene ligands in µ3-modes and encapsulated two mutually twisted tetramolybdates. Heterometallic nanocage contains a 54-Ag-atom outer ellipsoid silver cage decorated by 12 copper inside wall. Nanosized Ag54Cu12 is a n-type narrow-band-gap semiconductor with a good photocurrent response. Preliminary experiments demonstrates that Ag54Cu12 itself and activated carbon supported Ag54Cu12/C are effective catalysts for 1,3-dipole cycloaddition between alkynes and azides at ambient conditions. The work provides not only a new synthetic route toward Ag(I)-Cu(I) nanoclusters but also an important heterometallic intermediate in CuAAC catalytic reaction.

Discovering of Atomically Precise Metal Nanoclusters by High-Throughput Syntheses Platform

Understanding the complete structure of noble metal nanoclusters is both academically and practically significant. However, progress has been hindered by the low synthetic efficiency of many nanocluster syntheses. In this study, we present the first high-throughput syntheses of homo-gold, homo-copper, and gold-copper alloy nanoclusters in dichloromethane at room temperature. Through high-throughput screening, we successfully obtained three nanoclusters in a single reaction: Au18(SC6H11)14, [Au41Cu66(SC6H11)44](SbF6)3, and an unidentified copper cluster (referred to as Au18, Au41Cu66 , and Cu-NC). The optimized synthesis route was achieved with the assistance of machine learning for experimental data analysis, which also guided the synthesis of other metal nanoclusters such as Au40Cu34(4-S-PhF)40 (Au40Cu34), [Au6Cu6(SPh)12]n ([Au6Cu6]n), and Au18Cu32(3,5-C8H9S)36 (Au18Cu32)). This research demonstrates that high-throughput screening can be a valuable tool in accelerating the development of nanocluster syntheses.

Bimetallic Ag125Cu8 Nanocluster, Structure Determination, and Nonlinear Optical Properties

The atomic precision of the subnanometer nanoclusters has provided sound proof on the structural correlation of metal complexes and larger-sized metal nanoparticles. Herein, we report the synthesis, crystallography, structural characterization, electrochemistry, and optical properties of a 133-atom intermetallic nanocluster protected by 57 thiolates (3-methylbenzenethiol, abbreviated as m-MBTH) and 3 chlorides, with the formula of Ag125Cu8(m-MBT)57Cl3. This is the largest Ag-Cu bimetallic cluster ever reported. Crystallographic analysis revealed that the nanocluster has a three-layer concentric core-shell structure, Ag7@Ag47@Ag71Cu8S57Cl3, and the Ag54 metal kernel adopts a D5h symmetry. The nuclei number is between that of the previously reported large silver cluster [Ag136(SR)64Cl3Ag0.45]- and the large silver-rich cluster Au130-xAgx(SR)55 (x = 98). All these three clusters bear a similar metallic core structure, while the main structural difference lies in the shell motif structures. Electron counting revealed an open electron shell with 73 delocalized electrons, which was verified by the electron paramagnetic resonance analysis. The DPV electrochemical measurement indicates a multielectron state quantization double-layer charging shape and single-electron sequential charging and discharging characteristic of the AgCu alloy cluster. In addition, the open-hole Z-scan test reveals the nonlinear optical absorption (2-3 optical absorption in the NIR-II/III region) of Ag125Cu8 nanoclusters.

Stepwise structural evolution toward robust carboranealkynyl-protected copper nanocluster catalysts for nitrate electroreduction

Atomically precise metal nanoclusters (NCs) are emerging as idealized model catalysts for imprecise metal nanoparticles to unveil their structure-activity relationship. However, the directional synthesis of robust metal NCs with accessible catalytic active sites remains a great challenge. In this work, we achieved bulky carboranealkynyl-protected copper NCs, the monomer Cu13·3PF6 and nido-carboranealkynyl bridged dimer Cu26·4PF6, with fair stability as well as accessible open metal sites step by step through external ligand shell modification and metal-core evolution. Both Cu13·3PF6 and Cu26·4PF6 demonstrate remarkable catalytic activity and selectivity in electrocatalytic nitrate (NO3-) reduction to NH3 reaction, with the dimer Cu26·4PF6 displaying superior performance. The mechanism of this catalytic reaction was elucidated through theoretical computations in conjunction with in situ FTIR spectra. This study not only provides strategies for accessing desired copper NC catalysts but also establishes a platform to uncover the structure-activity relationship of copper NCs.

Doping effect on a two-electron silver nanocluster

This study investigates the effects of metal addition and doping of a 2-electron silver superatom, [Ag10{S2P(OiPr)2}8] (Ag10). When Ag+ is added to Ag10 in THF solution, [Ag11{S2P(OiPr)2}8(OTf)] (Ag11) is rapidly formed almost quantitatively. When the same method is used with Cu+, a mixture of alloys, [CuxAg11-x{S2P(OiPr)2}8]+ (x = 1-3, CuxAg11-x), is obtained. In contrast, introducing Au+ to Ag10 leads to decomposition. The structural and compositional analysis of Ag11 was characterized by single-crystal X-ray diffraction (SCXRD), ESI-MS, NMR spectroscopy, and DFT calculations. While no crystal structure was obtained for CuxAg11-x, DFT calculations provide insights into potential sites for copper location. The absorption spectrum exhibits a notable blue shift in the low-energy band after copper doping, contrasting with that of the slight shift observed in 8-electron Cu-doped Ag nanoclusters. Ag11 and CuxAg11-x are strongly emissive at room temperature, and solvatochromism across different organic solvents is highlighted. This study underscores the profound influence of metal addition and doping on the structural and optical properties of silver nanoclusters, providing important contributions to understanding the nanoclusters and their photophysical behaviors.

Thiacalix[4]arene Etching of an Anisotropic Cu70H22 Intermediate for Accessing Robust Modularly Assembled Copper Nanoclusters

Atom-precise metal nanoclusters (NCs) with large bulk (nuclearity >60) are important species for insight into the embryonic phase of metal nanoparticles and their top-down etching synthesis. Herein, we report a metastable rod-shaped 70-nuclei copper-hydride NC, [Cl@Cu70H22(PhC≡C)29(CF3COO)16]2+ (Cu70), with Cl- as the template, in which the Cl@Cu59 kernel adopts a distinctive metal packing mode along the bipolar direction, and the protective ligand shell exhibits corresponding site differentiation. In terms of metal nuclearity, Cu70 is the largest alkynyl-stabilized Cu-hydride cluster to date. As a typical highly active intermediate, Cu70 could undergo a transformation into a series of robust modularly assembled Cu clusters (B-type Cu8, A-A-type Cu22, A-B-type Cu23, and A-B-A-type Cu38) upon etching by p-tert-butylthiacalix[4]arene (H4TC4A), which could not be achieved by "one-pot" synthetic methods. Notably, the patterns of A and B blocks in the Cu NCs could be effectively modulated by employing appropriate counterions and blockers, and the modular assembly mechanism was illustrated through comprehensive solution chemistry analysis using HR-ESI-MS. Furthermore, catalytic investigations reveal that Cu38 could serve as a highly efficient catalyst for the cycloaddition of propargylic amines with CO2 under mild conditions. This work not only enriched the family of high-nuclear copper-hydride NCs but also provided new insights into the growth mechanism of metal NCs.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Icosidodecahedral Coordination-Saturated Cuprofullerene

The first coordination-saturated buckyball with a C60 molecule totally encased in an icosidodecahedral Cu30 in a (μ30 -(η2 )30 )-fashion, namely C60 @Cu30 @Cl36 N12 , has been successfully realized by a C60 -templated assembly. The 48 outmost coordinating atoms (36Cl+12N) comprise a new simple polyhedron that is described by a ccf topology. Charge transfer from (CuI , Cl) to C60 explains the expansion of the light absorption up to 700 nm, and accounts for an ultrafast photophysical process that underpins its high photothermal conversion efficiency. This work makes a giant step forward in exohedral metallofullerene (ExMF) chemistry.

Alkynyl-Protected Bimetallic Nanoclusters with a Hybrid Mackay Icosahedral Ag42 Cu12 Cl Kernel and an Octahedral Ag22 Cu12 Kernel

A facile strategy that directly reduces alkynyl-silver precursors and copper salts for the synthesis of bimetallic nanoclusters using the weak reducing agent Ph2 SiH2 is demonstrated. Two alkynyl-protected concentric-shell nanoclusters, (Ph4 P)2 [Ag22 Cu12 (C≡CR)28 ] and (Ph4 P)3 [Ag42 Cu12 Cl(C≡CR)36 ] (Ag22 Cu12 and Ag42 Cu12 Cl, R=bis(trifluoromethyl)phenyl), were successfully obtained and characterized by single-crystal X-ray diffraction and electro-spray ionization mass spectrometry. For the first time, a hybrid 55-atom two-shell Mackay icosahedron was found in Ag42 Cu12 Cl, which is icosahedral M54 Cl instead of M55 . The incorporation of a chloride in the metal icosahedron contributes to the stability of the cluster from both electronic and geometric aspects. Alkynyl ligands show various binding-modes including linear "RC≡C-Cu-C≡CR" staple motifs.

Alloying and dealloying of Au18Cu32 nanoclusters at precise locations via controlling the electronegativity of substituent groups on thiol ligands

The doping site of metals in an alloy nanocluster plays a key role in determining the cluster properties. Herein, we found that alloying engineering was achieved by replacing Cu at specific positions in the second layer Cu₂₀ shell of the [Au18Cu32(SR-O)36]2- or [Au18Cu32(SR-F)36]3- (SR-O = -S-PhOMe; SR-F = -SC₆H₃^3,4F₂) nanocluster with Au to generate a core-shell [Au20.31Cu29.69(SR-O)36]2- protected by mercaptan ligands with electron-donating substituents, which could be stable obtained compared with the alloyed nanocluster with electron-withdrawing substituent ligands. Moreover, dealloying engineering was accomplished by an electron-withdrawing substituent ligand exchange strategy (i.e., [Au18Cu32(SR-F)36]2-). The abovementioned reaction was analyzed using single-crystal X-ray crystallography, electrospray ionization mass spectrometry, and X-ray photoelectron spectroscopy and monitored via time-dependent ultraviolet-visible absorption spectroscopy. This reversible and precise location of alloying and dealloying provides the possibility for studying the relationship between the structure and properties of nanoclusters at the atomic level.

A bimetallic Ag15Cu12(S-c-C6H11)18(CH3COO)3 nanocluster featuring an irregular Ag12 kernel

Here, we report the synthesis and atomic structure of a Ag₁₅Cu₁₂(SR)₁₈(CH₃COO)₃·(C₆H₁₄) nanocluster (Ag₁₅Cu₁₂ for short, SR denotes cyclohexanethiol), confirmed by single-crystal X-ray diffraction (SC-XRD), electrospray ionization mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). X-ray crystallographic analysis revealed that Ag₁₅Cu₁₂ consisted of an irregular Ag₁₂ core, stabilized by the Ag₃Cu₁₂(SR)₁₈(CH₃COO)₃ shell. The shell consisted of two nearly planar Cu₃(SR)₆ moieties, three monomeric [-SR-Ag-SR-] units and three Cu₂(CH₃COO) staples. Furthermore, time-dependent density functional theory (TD-DFT) simulation was performed to interpret the optical absorption features of Ag₁₅Cu₁₂. Overall, this work will broaden and deepen the understanding of Ag-Cu alloy nanoclusters.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Regulation of Surface Structure of [Au9Ag12(SAdm)4(Dppm)6Cl6](SbF6)3 Nanocluster via Alloying

Tailoring of specific sites on the nanocluster surface can tailor the properties of nanoclusters at the atomic level, for the in-depth understanding of structure and property relationship. In this work, we explore the regulation of surface structure of [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ nanocluster via alloying. We successfully obtained the well-determined tri-metal [Au₉Ag₈@Cu₄(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ by the reaction of [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ with the Cu^I(SAdm) complex precursor. X-ray crystallography identifies that the Cu dopants prioritily replace the position of the silver capped by Dppm ligand in the motif. The Cu doping has affected the optical properties of Au₉Ag₁₂ alloy nanocluster. DPV spectra, CD spectra and stability tests suggest that the regulation of surface structure via Cu alloying changes the electronic structure, thereby affecting the electrochemical properties, which provides insight into the regulation of surface structure of [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃via alloying.

Electrochemical CO2 reduction catalyzed by atomically precise alkynyl-protected Au7Ag8, Ag9Cu6, and Au2Ag8Cu5 nanoclusters: probing the effect of multi-metal core on selectivity

We report the first all-alkynyl-protected Au2Ag8Cu5 cluster, which adopts a M@M8@M6 core configuration similar with Au7Ag8/Ag9Cu6 clusters. The three clusters exhibited strong metal core effect toward CO2RR, which was understood by DFT calculations.

A homoleptic alkynyl-protected [Ag9Cu6( t BuC[triple bond, length as m-dash]C)12]+ superatom with free electrons: synthesis, structure analysis, and different properties compared with the Au7Ag8 cluster in the M15 + series

We report the first homoleptic alkynyl-protected AgCu superatomic nanocluster [Ag9Cu6( t BuC[triple bond, length as m-dash]C)12]+ (NC 1, also Ag9Cu6 in short), which has a body-centered-cubic structure with a Ag1@Ag8@Cu6 metal core. Such a configuration is reminiscent of the reported AuAg bimetallic nanocluster [Au1@Ag8@Au6( t BuC[triple bond, length as m-dash]C)12]+ (NC 2, also Au7Ag8 in short), which is also synthesized by an anti-galvanic reaction (AGR) approach with a very high yield for the first time in this study. Despite a similar Ag8 cube for both NCs, structural anatomy reveals that there are some subtle differences between NCs 1 and 2. Such differences, plus the different M1 kernel and M6 octahedron, lead to significantly different optical absorbance features for NCs 1 and 2. Density functional theory calculations revealed the LUMO and HOMO energy levels of NCs 1 and 2, where the characteristic absorbance peaks can be correlated with the discrete molecular orbital transitions. Finally, the stability of NCs 1 and 2 at different temperatures, in the presence of an oxidant or Lewis base, was investigated. This study not only enriches the M15 + series, but also sets an example for correlating the structure-property relationship in alkynyl-protected bimetallic superatomic clusters.

Structure Determination of the Cl-Enriched [Ag52(SAdm)31Cl13]2+ Nanocluster

Cl atoms can serve as the innermost core, the peripheral ligand, or the counterions of metal nanoclusters. Herein, we report the structural determination a Cl-enriched [Ag₅₂(SAdm)₃₁Cl₁₃]²⁺. The ratio of Cl to AdmSH is quite high compared to those of other nanoclusters. Structurally, nine Cl atoms, existing at the interlayer of the inner kernel and the surface motif, serve as the bridging ligands to sustain the robustness of the whole structure. Interestingly, four Cl atoms on the motif structure can be substituted by Br. This work allows us to clear the regulation of Cl ligands in the structural construction of metal nanoclusters.

Total Structure of Bimetallic Core-Shell [Au42 Cd40 (SR)52 ]2- Nanocluster and Its Implications

Bimetallic core-shell nanostructures hold great promise in elucidating the bimetallic synergism. However, it remains a challenge to construct atomically precise core-shell with high-valence active metals on the gold surface. In this work, we report the total structure of a [Au₄₂ Cd₄₀ (SR)₅₂ ]^2- core-shell nanocluster and multiple implications. Single crystal X-ray diffraction (SCXRD) reveals that the structure possesses a two-shelled Au₆ @Au₃₆ core and a closed cadmium shell of Cd₄₀ , and the core-shell structure is then protected by 52 thiolate (-SR) ligands. The composition of the nanocluster is further confirmed by electrospray ionization mass spectrometry (ESI-MS). A catalytic test for styrene oxidation and a comparison with relevant nanoclusters reveal the surface effect on the catalytic activity and selectivity.

Heterometallation of Photoluminescent Silver(I) Sulfide Nanoclusters Protected by Octahedral Iridium(III) Thiolates

The recently-increasing interest in coinage metal clusters stems from their photophysical properties, which are controlled via heterometallation. Herein, we report homometallic Ag^I ₄₆ S₁₃ clusters protected by octahedral fac-[Ir(aet)₃ ] (aet=2-aminoethanethiolate) molecules and their conversion to heterometallic Ag^I ₄₃ M^I ₃ S₁₃ (M=Cu, Au) clusters. The reactions of fac-[Ir(aet)₃ ] with Ag⁺ and penicillamine produced [Ag₄₆ S₁₃ {Ir(aet)₃ }₁₄ ]²⁰⁺ ([1]²⁰⁺ ), where a spherical Ag^I ₄₆ S₁₃ cluster is covered by fac-[Ir(aet)₃ ] octahedra through thiolato bridges. [1]²⁰⁺ was converted to [Ag₄₃ M₃ S₁₃ {Ir(aet)₃ }₁₄ ]²⁰⁺ ([1^M ]²⁰⁺ ) with an Ag^I ₄₃ M^I ₃ S₁₃ cluster by treatment with M⁺ , retaining its overall structure. [1]²⁰⁺ was photoluminescent and had an emission band ca. 690 nm that originated from an S-to-Ag charge transfer. While [1^Cu ]²⁰⁺ showed an emission band with a slightly higher energy of ca. 650 nm and a lower quantum yield, the emission band for [1^Au ]²⁰⁺ shifted to a much higher energy of ca. 590 nm with an enhanced quantum yield.

Tailoring silver nanoclusters via doping: advances and opportunities

Atomically precise noble metal nanoclusters (especially Au and Ag) have been pursued due to their fascinating molecule-like properties. In spite of the significant progress on Au nanoclusters (NCs), the structure and property evolution of Ag NCs is still in high demand. Doping is a useful strategy for improving the physicochemical performances of Ag NCs. Herein we summarize the recent advances in tailoring silver NC structures and properties via doping. First, we reviewed the recent studies on the synthesis of hetero metal atom doped silver bimetallic nanoclusters, which are classified by the dopants, including Au, Pt, Pd, Cu, Ni and Cd. Second, the doping effects on their properties were reviewed, including the locations of hetero metal atoms, the influence on their stability, and the charge state evolution. Moreover, we highlighted the doping-dependent improvement of the photo-luminescence (PL) performance and catalytic activity of Ag NCs.

Intercluster exchanges leading to hydride-centered bimetallic clusters: a multi-NMR, X-ray crystallographic, and DFT study

Encouraged by the successful syntheses of alloy nanoclusters (or nanoparticles) via intercluster (or interparticle) reactions, herein we apply this methodology to prepare a series of bimetallic hydride clusters. Mixing of two clusters, [Ag₇(H){E₂P(OⁱPr)₂}₆] (E = S, 1; Se, 3) and [Cu₇(H){E₂P(OⁱPr)₂}₆] (E = S, 2; Se, 4), yields two series of hydride-centered bimetallic clusters, [Cu_xAg_7-x(H){E₂P(OⁱPr)₂}₆] (x = 0-7; E = S, 5; Se, 6). Their compositions are fully characterized by positive-mode ESI-MS spectrometry, multi-NMR spectroscopy, and the structures of [Cu₆Ag(H){S₂P(OⁱPr)₂}₆] (5a) and [CuAg₆(H){Se₂P(OⁱPr)₂}₆] (6a) by single crystal X-ray diffraction. The presence of individual compounds in solution is the result of a (dynamic) chemical equilibrium primarily driven by metal exchanges. In fact, the process of inter-cluster exchange of 1 and 2 leading to hydride-centered bimetallic clusters 5 can be monitored by concentration-dependent ³¹P NMR spectroscopy of which the higher concentration of 1 in the reaction, the closer to its resonance will be the distribution, in accord with Le Chatelier's principle. The dynamic equilibrium is further confirmed by 2D exchange spectroscopy that reveals a stepwise process involving one metal exchange at a time. DFT calculations on a model series of clusters 6 show that silver prefers occupying the inner tetrahedral positions, while copper favors capping positions, in full agreement with the crystal structure of 5a and 6a.

Total structural determination of alloyed Au15.37Cu16.63(S-Adm)20 nanoclusters with double superatomic chains

Thiolated-alloy nanocluster Au15.37Cu16.63(S-Adm)20 ((AuCu)32 for short) has been synthesized. Single crystal X-ray crystallography (SC-XRD) proved that this cluster contains a Au14Cu6 core, which is composed of double superatom chains, two M4(SR)5 (M = Au/Cu) motifs, four Cu(SR)2 monomer staples and two SR molecules at the waist. The composition of this nanocluster is confirmed by SC-XRD and further verified by XPS, EDX and 2H-NMR. Surprisingly, double superatom chains connect to each other only via two Au-Au bonds, which makes the kernel resemble a tunnel. Combined with DFT calculation and electronic structure analysis, it is further proved that the (AuCu)32 nanocluster contains six 2e alloy superatomic Au3Cu2+ units. This work is the first report showing that superatom units (CuAu32+) self-assembling to a hollow kernel maintain the superatom characteristic of metal nanoclusters, which enriches the fundamental knowledge of metal superatom clusters. The stable electronic structure of the nanocluster provides an experimental basis for theoretical analysis in the future. In addition, the hollow structure may be promising in catalytic applications.

[AuAg26(SR)18S]- Nanocluster: Open Shell Structure and High Faradaic Efficiency in Electrochemical Reduction of CO2 to CO

For atomically precise metal nanoclusters, distinctive molecular architectures and promising applications are urgently required to be intensively explored. Herein, we have first reported the open shell structure of the [AuAg₂₆(S-Adm)₁₈S]^- nanocluster and its application in the electrochemical reduction of CO₂. The X-ray crystal structure of the AuAg₂₆ nanocluster is composed of a AuAg₁₂ icosahedron kernel and a Ag₁₄(SR)₁₈S open shell. The shell includes a Ag₆(SR)₃S, a Ag₅(SR)₆, and three Ag(SR)₃ motifs. It is the first time twisty propeller-like Ag₅(SR)₆ and trefoil-like Ag₆(SR)₃S motifs in metal nanoclusters have been observed. Due to the novel open shell configuration of Ag₁₄(SR)₁₈S, four triangular facets of the kernel are exposed. The AuAg₂₆ nanocluster shows excellent catalytic activity in the electrochemical reduction of CO₂ to CO. The Faradaic efficiency of CO is up to 98.4% under -0.97 V. The electrochemical in situ infrared study and DFT calculations demonstrate that the open shell structure of the AuAg₂₆ nanocluster is beneficial to the forming of intermediate COOH* in the electrochemical reduction of CO₂ to CO.

New Routes for Multicomponent Atomically Precise Metal Nanoclusters

Atomically precise metal nanoclusters (NCs), protected by a monolayer of ligands, are regarded as potential building blocks for advanced technologies. They are considered as intermediates between the atomic/molecular regime and the bulk. Incorporation of foreign metals in NCs enhances several of their properties such as catalytic activity, luminescence, and so on; hence, it is of high importance for tuning their properties and broadening the scope of applications. In most of the cases, enhancement in specific properties was observed upon alloying due to the synergistic effect. In the past several years, many alloy clusters have been synthesized, which show a tremendous change in the properties than their monometallic analogs. However, controlling the synthesis and tuning the structures of alloy NCs with atomic precision are major challenges. Various synthetic methodologies have been developed so far for the controlled synthesis of alloy NCs. In this perspective, we have highlighted those diverse synthetic routes to prepare alloys, which include co-reduction, galvanic reduction, antigalvanic reduction, metal deposition, ligand exchange, intercluster reaction, and reaction of NCs with bulk metals. Advancement in synthetic procedures will help in the preparation of alloy NCs with the desired structure and composition. Future perceptions concerning the progress of alloy nanocluster science are also provided.

A construction guide for high-nuclearity (≥50 metal atoms) coinage metal clusters at the nanoscale: bridging molecular precise constructs with the bulk material phase

Synthesis remains a major strength in chemistry and materials science and relies on the formation of new molecules and diverse forms of matter. The construction and identification of large molecules poses specific challenges and has historically lain in the realm of biological (organic)-type molecules with evolved synthesis methods to support such endeavours. But with the development of analytical tools such as X-ray crystallography, new synthesis methods toward large metal-based (inorganic) molecules and clusters have come to the fore, making it possible to accurately determine the precise distribution of hundreds of atoms in large clusters. In this review, we focus on different synthesis protocols used to form new metal clusters such as templating, alloying and size-focusing strategies. A specific focus is on group 11 metals (Cu, Ag, Au) as they currently predominate large metal cluster investigations and related Au and Ag bulk surface phenomena. This review focuses on metal clusters that have very high-nuclearity, i.e. with 50 or more metal centers within the isolated cluster. This size domain, it is believed, will become increasingly important for a variety of applications as these metal clusters are positioned at the interface between the molecular and bulk phases, whilst remaining a classic nanomaterial and retaining unique nano-sized properties.

The geometric and electronic structures of a Ag13Cu10(SAdm)12X3 nanocluster

Herein, we report the synthesis and total structure of a Cu-rich alloy nanocluster protected by twelve adamantanethiolate ligands, i.e., [Ag₁₃Cu₁₀(SAdm)₁₂]X₃ (-SAdm = SC₁₀H₁₅, X = counterion), which was confirmed by single-crystal X-ray structure determination and electrospray ionization mass spectrometry (ESI-MS). X-ray crystallographic analysis indicated that [Ag₁₃Cu₁₀(SAdm)₁₂]X₃ consisted of an icosahedral Ag₁₃ core, covered by a cage-like shell of Cu₁₀(SAdm)₁₂. Furthermore, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the geometric and electronic structures and KS orbitals and UV-vis spectroscopy were performed on the model [Ag₁₃Cu₁₀(SMe)₁₂]³⁺ and its monometallic analog [Ag₂₃(SMe)₁₂]³⁺. This work will deepen the understanding of core-shell Ag-Cu alloy nanoclusters.